High-speed operation
Paul P. Acarnley · Institution of Engineering and Technology eBooks · 2002
In many applications the motor must be able to produce a large pull-out torque over a wide range of stepping rates, so the time taken to position a load is minimised. At high stepping rates each phase is excited for only a short time interval and the build-up time of the phase current is a significant proportion of the excitation interval. When a motor is operating at the highest speeds the current in each phase may not even reach its rated value before the excitation interval finishes and the phase is turned off. In addition the time taken for the phase current to decay becomes important at high speeds, because the phase current continues flowing (through the freewheeling diode) beyond the excitation interval dictated by the drive transistor switch.